The thumbnail size and the Album thumbnail size were pre-filled with 200 and 250 after I activated the plugin. I didn’t change the default values and there’s no px in the fields.
I guess the error wasn’t caused by these two fields in my case.
Thank you mkto for your reply.
I think what you described is the same as what plugin author has instructed us to do.
The link that generated by wordpress is the same as the slug.
Still doesn’t work.